The purpose of this project is to investigate the genetic regulation of the galactose catabolic enzymes, galactokinase (GALK), galactose-1-phosphate uridyl transferase (GALT), and UDP-galactose-4-epimerase (GALE) in a mammalian cell culture system. The level of GALK and GALT have been determined in dividing cells growing in hexose-free media supplemented with glucose or galactose. There is a 1.6 to 2.0 fold increase in GALK activity, and 1.2 to 1.6 fold increase in GALT activity when cells are grown with galactose as a hexose source as compared to those grown in glucose. The response of the third enzyme in the pathway, GALE, to the presence of galactose in the media is currently being studied. In addition, the effect of SV-40 transformation of cells on the increased enzyme activity is also being investigated. The effects of galactose and glucose in the growth media upon the uptake of galactose by cells is also being studied. Growing cells in galactose for 24 hours increases the amount of 14C-galactose taken up by these cells 1.5 to 1.6 times that which is taken up by cells growing in glucose. The effect of SV-40 transformation on the rate of uptake of galactose is currently being investigated.